Effects of water content on sugar metabolism of Malus × robusta seed cryopreservation

Water content is a key factor influencing the seed cryopreservation, but its effecting mechanism is not fully understood. In order to explore the effect and way of water content on the viability of seed cryopreservation on viability, Malus × robusta seeds with different water contents were obtained by silica gel. The seed viability, sugar content and related enzyme indexes before and after cryopreservation were measured and correlation analysis were done. The results were as follows: (1) After 15 days of cryopreservation, the viability of seeds with different water contents was different, and the viability of seeds showed a trend of increasing and then decreasing as the water content of seeds decreased, and the seeds with 9.02% water content had the highest germination rate, at 53.33%. But after 120 days of cryopreservation, the viability of seeds increased as the water content decreased, and the seeds with 6.40% water content got the highest germination rate, at 27.78%. This indicates that the water content of Malus × robusta seeds has a significant effect on the viability after cryopreservation. It is affected by the storage time in liquid nitrogen, and the optimum water content decreases as the storage time extended in liquid nitrogen. (2) Correlation analysis showed that there was a significant negative correlation between water content and viability (r=-0.82). There was significant negative correlation with fructose and sucrose content, acid invertase, fructokinase, while seed germination rate was significantly positive correlation with these indexes, suggesting that water content affects the contents of sucrose and fructose through effecting the activity of acid converting enzymes, which in turn affects sucrose metabolism to respond to low temperature and dehydration stress, ultimately leading to differences in viability. The seed viability was also affected by fructose metabolism through fructose kinase. Besides, alginate was one of the important regulatory substances of Malus × robusta seed in response to water and low temperature stresses. In summary, water content has a significant effect on the viability of Malus × robusta seeds cryopreservation through the combined effects of sucrose and fructose metabolism. This study provides a theoretical reference to further explore the cryopreservation mechanism of seed.